Alternator Not Enough (Upgrade recommendations)

[ykf7b0]

I'm needing some help with the charging system on my 69 roadrunner 440 with electronic ignition conversion and electric fuel pump. I have already upgraded the wiring and did the ammeter bypass trick. I went from square back alternator to 75 amp Powermaster and at idle I'm still slowly discharging. I'm thinking that a Denso might be a better unit for my setup. Are any of you running a Denso and if so, what did it involve and which Denso are you using? Internally or externally regulated? Thank to all!!!

 

[old_skool]

If your still dis-charging, you have a short somewhere, and a stronger alt won't stop that, when I upgrade though, I plan on using a Grand Cherokee 136amp alt, might need some mods for the brackets etc.

 

[ykf7b0]

If your still dis-charging, you have a short somewhere, and a stronger alt won't stop that, when I upgrade though, I plan on using a Grand Cherokee 136amp alt, might need some mods for the brackets etc.

I quess I should say not charging at idle which is resulting in my discharge. I have verified that no shorts exist through varies test with the voltmeter. I am convinced that the additional draw of the high volumn fuel pump is the culprit. I have other accessories such as an electric fan and nitrous bottle heater that are seldom turned on. I'm looking for advice on an alternator that can handle the job of providing many amps at idle speed.

 

[Nsane]

I am running a small denso unit i believe it was for a mid to late 90's impalla ss. took a little figuring to find the correct model and wiring but it works great it is 105 amp small and fit right in the factory spot with very little effort. You should be able to see it in the pictures on my build thread just search my name. If you are intersted i could get you the information and wiring instructions. after the weekend not sure if i have them at work but maybe. PM me and i can get you everything if you want it is a very clean and nice install and the plugs are available at oriley's, carquest or nappa.

 

[HEMI-ITIS]

You could try a smaller pulley:blob1:

 

[Nsane]

This is the best pic I have.

 

[Cranky]

What is your idle rpm? What are the conditions that you notice discharge? Depending on what you have running, most alternators won't charge a lot at idle and if the rpm is on the low side, it just compounds the problem. Night time running with lights, ac, stereo, electric fuel pump etc take a pretty good amount of current and sitting at a light in gear will most likely show discharge.

 

[69Bee]

There is an amperage adjustment screw on the driver side of the carb. Turn it in a little to make the alternator charge more...

On a more serious note, your 136 Amp alternator does not put out 136 amps UNLESS the load requires it. Have you ever looked at the regulator? Put the race blue 732 regulator on; it helped my car out.

 

[Meep-Meep]

I'm pretty sure this will provide enough power

 

[ykf7b0]

- - - Updated - - -

Thanks Nsane! I will pm later. Is anyone else using the Denso two field?

I meant to say Denso externally regulated.

 

[66chargerpat]

I'm using a denso for a 97 cummins dodge truck. It has the dual pulley and the dual field posts. It wired up with 70's externally regulater. I run a 4 gauge wire straight to the battery. Some people even run a 150-200 amp. breaker also.

 

[khryslerkid]

What's the amp meter bypass trick? And are you checking your voltage drop at the battery with a voltage meter? If so what are your readings at idol verses a higher rpm?

 

[ykf7b0]

What's the amp meter bypass trick? And are you checking your voltage drop at the battery with a voltage meter? If so what are your readings at idol verses a higher rpm?

Thanks chargerpat! The ammeter bypass is to eliminate the weakest point in the older Mopar charging system. You simply put both the in and out ring terminals on the ammeter input post if I remember correctly. This will render the ammeter useless but you want to install a voltmeter anyway. Voltage drop is read at battery with voltmeter and is reading 12.6 at idle and upward if I hit the accelerator hard, but then will descend down to around 12.3 and possibly lower depending on how long it idles. Headlights are useless at this point. At highway speed I'm around 14.0 volts.

 

[Badvert65]

You could try a smaller pulley:blob1:

I was just going to suggest that. Had a similar problem with some John Deere tractors. They are diesel and run at low rpm's. I put a smaller pulley on the Alt and that fixed things right up.

 

[Cranky]

Thanks chargerpat! The ammeter bypass is to eliminate the weakest point in the older Mopar charging system. You simply put both the in and out ring terminals on the ammeter input post if I remember correctly. This will render the ammeter useless but you want to install a voltmeter anyway. Voltage drop is read at battery with voltmeter and is reading 12.6 at idle and upward if I hit the accelerator hard, but then will descend down to around 12.3 and possibly lower depending on how long it idles. Headlights are useless at this point. At highway speed I'm around 14.0 volts.

Have you taken that alternator to have it checked?

 

[ykf7b0]

Have you taken that alternator to have it checked?

No. It is a Powermaster 75 amp I just don't believe it is putting out enough amps at idle rpm with my accessories and I've read that other users have experienced this as well. The Denso seems to be the hot setup for lots of folks. I would love for someone to chime in that has made this conversion on a big block. Thanks Cranky!

 

[Herr_Poopschitz]

75 amps is waaaay more than your needs. Depending on your pump, figure it draws ~5 to 10 amps MAX.

The alternator is not the problem...as others have stated, sounds like it just needs to turn faster at idle.

 

[ykf7b0]

I agree with this but it seems that if I can get an alternator that will produce more at idle then I would be where I need to be. I could throttle the Powemaster to 3000 rpm or put a smaller pulley on it but I'm leaning toward a Denso that is claimed by others to jump their voltage reading from say 12.0 at idle to 13.9 or 14.2. Thanks!

 

[69Bee]

I agree with this but it seems that if I can get an alternator that will produce more at idle then I would be where I need to be. I could throttle the Powemaster to 3000 rpm or put a smaller pulley on it but I'm leaning toward a Denso that is claimed by others to jump their voltage reading from say 12.0 at idle to 13.9 or 14.2. Thanks!

What you don't seem to understand is that even if you put an alternator on that can produce 10,000 amps, it will NEVER do it unless the load requires it. Your 75 amp alt is way more than enough, but there are other issues at hand. You have never mentioned what regulator you are using. The blue MP Performance 732 unit will allow the system to charge 14.2v at idle. If you are still using the old point type unit, it is crap, and causes the issues that you are having.

You mention running at 14v on the highway, but 12ish at idle. Is your pulley possibly too big on the aftermarket alternator? Again, it doesn't matter how big the alternator is, it will only produce that rating under a full load. If there is no real load, there will be little power output.

 

[sleepar]

At least an 8 ga wire from the alt to the battery then to you're loads... I hate to imagine that running through the original wire harness and amp gauge....